1 /* $OpenBSD: auth2-hostbased.c,v 1.18 2014/07/15 15:54:14 millert Exp $ */ 2 /* 3 * Copyright (c) 2000 Markus Friedl. All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 15 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 16 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 17 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 18 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 19 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 20 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 21 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 23 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 24 */ 25 26 #include "includes.h" 27 28 #include <sys/types.h> 29 30 #include <pwd.h> 31 #include <string.h> 32 #include <stdarg.h> 33 34 #include "xmalloc.h" 35 #include "ssh2.h" 36 #include "packet.h" 37 #include "buffer.h" 38 #include "log.h" 39 #include "misc.h" 40 #include "servconf.h" 41 #include "compat.h" 42 #include "key.h" 43 #include "hostfile.h" 44 #include "auth.h" 45 #include "canohost.h" 46 #ifdef GSSAPI 47 #include "ssh-gss.h" 48 #endif 49 #include "monitor_wrap.h" 50 #include "pathnames.h" 51 52 /* import */ 53 extern ServerOptions options; 54 extern u_char *session_id2; 55 extern u_int session_id2_len; 56 57 static int 58 userauth_hostbased(Authctxt *authctxt) 59 { 60 Buffer b; 61 Key *key = NULL; 62 char *pkalg, *cuser, *chost, *service; 63 u_char *pkblob, *sig; 64 u_int alen, blen, slen; 65 int pktype; 66 int authenticated = 0; 67 68 if (!authctxt->valid) { 69 debug2("userauth_hostbased: disabled because of invalid user"); 70 return 0; 71 } 72 pkalg = packet_get_string(&alen); 73 pkblob = packet_get_string(&blen); 74 chost = packet_get_string(NULL); 75 cuser = packet_get_string(NULL); 76 sig = packet_get_string(&slen); 77 78 debug("userauth_hostbased: cuser %s chost %s pkalg %s slen %d", 79 cuser, chost, pkalg, slen); 80 #ifdef DEBUG_PK 81 debug("signature:"); 82 buffer_init(&b); 83 buffer_append(&b, sig, slen); 84 buffer_dump(&b); 85 buffer_free(&b); 86 #endif 87 pktype = key_type_from_name(pkalg); 88 if (pktype == KEY_UNSPEC) { 89 /* this is perfectly legal */ 90 logit("userauth_hostbased: unsupported " 91 "public key algorithm: %s", pkalg); 92 goto done; 93 } 94 key = key_from_blob(pkblob, blen); 95 if (key == NULL) { 96 error("userauth_hostbased: cannot decode key: %s", pkalg); 97 goto done; 98 } 99 if (key->type != pktype) { 100 error("userauth_hostbased: type mismatch for decoded key " 101 "(received %d, expected %d)", key->type, pktype); 102 goto done; 103 } 104 if (key_type_plain(key->type) == KEY_RSA && 105 (datafellows & SSH_BUG_RSASIGMD5) != 0) { 106 error("Refusing RSA key because peer uses unsafe " 107 "signature format"); 108 goto done; 109 } 110 service = datafellows & SSH_BUG_HBSERVICE ? "ssh-userauth" : 111 authctxt->service; 112 buffer_init(&b); 113 buffer_put_string(&b, session_id2, session_id2_len); 114 /* reconstruct packet */ 115 buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST); 116 buffer_put_cstring(&b, authctxt->user); 117 buffer_put_cstring(&b, service); 118 buffer_put_cstring(&b, "hostbased"); 119 buffer_put_string(&b, pkalg, alen); 120 buffer_put_string(&b, pkblob, blen); 121 buffer_put_cstring(&b, chost); 122 buffer_put_cstring(&b, cuser); 123 #ifdef DEBUG_PK 124 buffer_dump(&b); 125 #endif 126 127 pubkey_auth_info(authctxt, key, 128 "client user \"%.100s\", client host \"%.100s\"", cuser, chost); 129 130 /* test for allowed key and correct signature */ 131 authenticated = 0; 132 if (PRIVSEP(hostbased_key_allowed(authctxt->pw, cuser, chost, key)) && 133 PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b), 134 buffer_len(&b))) == 1) 135 authenticated = 1; 136 137 buffer_free(&b); 138 done: 139 debug2("userauth_hostbased: authenticated %d", authenticated); 140 if (key != NULL) 141 key_free(key); 142 free(pkalg); 143 free(pkblob); 144 free(cuser); 145 free(chost); 146 free(sig); 147 return authenticated; 148 } 149 150 /* return 1 if given hostkey is allowed */ 151 int 152 hostbased_key_allowed(struct passwd *pw, const char *cuser, char *chost, 153 Key *key) 154 { 155 const char *resolvedname, *ipaddr, *lookup, *reason; 156 HostStatus host_status; 157 int len; 158 char *fp; 159 160 if (auth_key_is_revoked(key)) 161 return 0; 162 163 resolvedname = get_canonical_hostname(options.use_dns); 164 ipaddr = get_remote_ipaddr(); 165 166 debug2("userauth_hostbased: chost %s resolvedname %s ipaddr %s", 167 chost, resolvedname, ipaddr); 168 169 if (((len = strlen(chost)) > 0) && chost[len - 1] == '.') { 170 debug2("stripping trailing dot from chost %s", chost); 171 chost[len - 1] = '\0'; 172 } 173 174 if (options.hostbased_uses_name_from_packet_only) { 175 if (auth_rhosts2(pw, cuser, chost, chost) == 0) 176 return 0; 177 lookup = chost; 178 } else { 179 if (strcasecmp(resolvedname, chost) != 0) 180 logit("userauth_hostbased mismatch: " 181 "client sends %s, but we resolve %s to %s", 182 chost, ipaddr, resolvedname); 183 if (auth_rhosts2(pw, cuser, resolvedname, ipaddr) == 0) 184 return 0; 185 lookup = resolvedname; 186 } 187 debug2("userauth_hostbased: access allowed by auth_rhosts2"); 188 189 if (key_is_cert(key) && 190 key_cert_check_authority(key, 1, 0, lookup, &reason)) { 191 error("%s", reason); 192 auth_debug_add("%s", reason); 193 return 0; 194 } 195 196 host_status = check_key_in_hostfiles(pw, key, lookup, 197 _PATH_SSH_SYSTEM_HOSTFILE, 198 options.ignore_user_known_hosts ? NULL : _PATH_SSH_USER_HOSTFILE); 199 200 /* backward compat if no key has been found. */ 201 if (host_status == HOST_NEW) { 202 host_status = check_key_in_hostfiles(pw, key, lookup, 203 _PATH_SSH_SYSTEM_HOSTFILE2, 204 options.ignore_user_known_hosts ? NULL : 205 _PATH_SSH_USER_HOSTFILE2); 206 } 207 208 if (host_status == HOST_OK) { 209 if (key_is_cert(key)) { 210 fp = key_fingerprint(key->cert->signature_key, 211 SSH_FP_MD5, SSH_FP_HEX); 212 verbose("Accepted certificate ID \"%s\" signed by " 213 "%s CA %s from %s@%s", key->cert->key_id, 214 key_type(key->cert->signature_key), fp, 215 cuser, lookup); 216 } else { 217 fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX); 218 verbose("Accepted %s public key %s from %s@%s", 219 key_type(key), fp, cuser, lookup); 220 } 221 free(fp); 222 } 223 224 return (host_status == HOST_OK); 225 } 226 227 Authmethod method_hostbased = { 228 "hostbased", 229 userauth_hostbased, 230 &options.hostbased_authentication 231 }; 232